Method and system for heat recovery from products of combustion and charge heating installation including the same

ABSTRACT

A plurality of independently flow rate-controlled flows of oxidant may be preheated at a heat exchanger (or both oxidant and fuel at separate heat exchangers) by heat exchange with a hot shell-side (heat transfer) fluid. The separate flows of hot oxidant are directed to associated separate burners where they combust with flows of fuel to produce hot combustion gases. The hot combustion gases are used to preheat the hot shell-side fluid at a recuperator or regenerator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 61/706,094 filed Sep. 26, 2012.

BACKGROUND

In processes which rely on delivery of large amounts of heat energy intoa furnace by combustion of a fuel, it is particularly important toachieve as high an energy-efficiency as possible. Thus it is a commonpractice to recover excess heat in the flue-gas, for example by using itto heat combustion air. Another way to improve efficiency is byoxy-combustion, which, by replacing air ordinarily used in combustionwith a stream that is largely oxygen, avoids heating the nitrogencomponent of air. While heat lost to the flue gas is reduced inoxy-combustion (because the flue-gas volume is less), the amount of heatlost is still substantial, and it would be advantageous to recover thatheat.

Heat recovery from oxycombustion in glass-making was discussed in detailin a study titled “Development of an advanced glass melting system: TheThermally Efficient Alternative Melter, TEAM. Phase 1, Finalreport.—Progress rept.” that was funded by the U.S. Department of Energy(DOE) and completed by Air Products under contract DE-AC02-89CE40917F(report number DOE/CE/40917-T2 published in February 1992 and availablefrom the National Technical Information Service of the U.S. government).In this report, the primary methods discussed were: 1) batch and cullet(i.e. glass-making raw materials) pre-heating, 2) natural gas reformingwith steam or CO₂, and 3) gas turbine cycles (where heat is converted togas compression for an air separation unit). Of these, the batch andcullet pre-heating options were found to offer the greatest improvementin efficiency. However, feedback from glassmakers indicated that batchand cullet pre-heating approaches had been tried and were foundextremely difficult due to clogging, mechanical complexity, andcontinual maintenance problems. Natural gas reforming with steam wasfound to offer good efficiency improvement and was recommended forfurther development.

In the automotive field, heat exchangers are known that allow transferof heat energy to multiple independent fluid flows. Such a heatexchanger is described by US2006/0266501. These are plate-type heatexchangers, which are not suitable for oxygen service for multiplereasons. For example, this type of heat exchanger does not provide asufficiently smooth flow path and is too difficult to manufacture withadequate cleanliness for oxygen service, and especially for hot oxygenservice. Cleanliness for hot oxygen service is of course greatlyimportant for safety reasons since the local highly oxidizingenvironment can pose an unacceptably high risk of uncontrolledcombustion.

U.S. Pat. No. 5,006,141 discloses cullet pre-heating schemes includingones where both cullet pre-heating and fuel pre-heating are combined.These schemes are subject to the difficulties of cullet pre-heatingdiscussed above.

U.S. Pat. No. 5,057,133 discloses a natural gas reforming scheme wherebyflue gas used to provide heat to the reformer is combined with a recyclestream from downstream of the reformer, in order to provide temperaturecontrol. Using a fluidized bed of hot sand to capture condensibles andrecycling the sand to the glass-making furnace is also described.

U.S. Pat. No. 5,714,132 discloses natural gas reforming using the fluegas itself as a source of steam and/or CO₂. While this concept appearsattractive in principle, in practice, sulfur and other catalyst poisonsin the flue gas are difficult to economically remove.

Although natural gas reforming was considered promising for heatrecovery, it has not been implemented. Whereas steam reforming is awell-known process, this application requires additional development,notably reformer tubes compatible with the condensation of sulfates andborates expected in the glass flue-gas stream, and burner technologysuited for the lower-energy-density fuel. These hurdles have proved toodaunting to allow the practical application of the concept.

Also mentioned in the above DOE report are the concepts of heating boththe oxygen and natural gas streams. The temperature limit for O₂pre-heating is given as 465° F. (240° C.), imposed by materialcompatibility with hot oxygen, while that for natural gas pre-heating isgiven as 750° F. (399° C.), imposed by the thermal cracking (carbonformation) of natural gas at higher temperatures.

An alternative to the schemes discussed above is the heating of oxygento temperatures above 240° C. However, heating the oxygen stream isextremely challenging, because the high reactivity of oxygen, especiallyat high temperature, places extreme constraints on the design andconstruction of the heat recovery system. For example, while it is acommon practice to use a regenerator, through which flue gas and airflow in alternating cycles in order to preheat the air, it is generallyconsidered impossible to use this technique with oxygen because of thefear that oxygen would react with contaminants inevitably present in theflue gas and deposited in the regenerator.

Another known solution is the use of ceramic heat exchangers. Thesesystems are usually intended to operate at temperatures of about 1000°C., where heat transfer is radiative. However, ceramic materials areknown to be fragile and ceramic heat exchangers are prone to leakage.Whereas minor leakage of air into the flue gas stream is acceptable,this is not the case for oxygen or fuel gas streams due to safetyissues. Thus, heat exchangers of this type are not acceptable forheating oxygen or fuel gas streams.

Thus, there is a need to provide a method and system for the recovery ofheat from products of combustion that is robust and not susceptible toleaks causing safety issues.

US 2009/0298002 discloses the use of a shell and tube heat exchangerwhere oxygen flows through the double-walled tubes while hot combustiongases flow through the shell. Contact between the hot combustion gases,which may include unburnt fuel, and the oxygen is inhibited not only bythe presence of the walls of the inner tubes but also by the presence ofthe walls of the outer tubes. The annular spaces between the ducts andtubes contain a static inert gas so that heat exchange first proceedsbetween the hot combustion gases and the inert gas and then between theinert gas and the oxygen. US 2009/0298002 does not address how the novelheat exchanger may be used in a furnace having multiple burners.Moreover, it suffers from the disadvantage of exhibiting a relativelylower heat exchange coefficient because each of the two separate phasesof heat exchange take place between a flowing fluid and a static fluid.

Thus, there is a need to provide a method and system for the recovery ofheat from products of combustion that includes multiple burners andwhich has a sufficiently high heat exchange coefficient.

U.S. Pat. No. 5,807,418 discloses heat recovery by “co-current indirectheat exchange” of an oxidant (at least 50% O₂) by the flue-gas, followedby using the partially-cooled flue-gas to pre-heat batch and/or cullet.As used by U.S. Pat. No. 5,807,418, “co-current indirect heat exchange”refers simply to a heat exchanger in which the oxidant and heatexchanger are separated by a wall, with both the oxidant and the fluegas flowing in the same direction. While a sketch is provided, detailssuch as materials of construction of the heat exchanger are not, but forthe comment that the heat exchanger is “constructed using materials andin a way that renders it compatible with and safe for handlingoxygen-rich oxidants and high temperatures”. Considering the practicaldifficulty of constructing such a heat exchanger, this instruction isnot sufficient to allow practical implementation by the skilled artisan.

Thus, there is a need to provide a method and system for the recovery ofheat from products of combustion that allows practical implementation byone of ordinary skill in the art.

US 2009/0084140 uses a scheme similar to U.S. Pat. No. 5,807,418, butwith batch/cullet pre-heat in parallel with oxidant pre-heat, and withadditional disclosure related to the batch/cullet heat exchanger. Again,no details on the construction of the oxidant heat exchanger aredisclosed. As best shown in FIG. 1, hot combustion gas FG is used topreheat oxygen O_(M) at a heat exchanger HX. The hot oxygen is splitinto three streams O_(A), O_(B), O_(C) each one of which is combustedwith a fuel stream F at an associated burner B to produce the hotcombustion gas FG. This approach suffers from the disadvantage that theflow rates of the individual oxygen streams can only be separatelycontrolled downstream of the oxygen heat exchanger. This means that theflow control devices are subjected to hot oxygen attack, leading topremature and potential catastrophic failure. This approach also suffersfrom the disadvantage that unburnt fuel in the hot combustion gases maycome into contact with oxygen, either from a leak or at a regenerator,thereby posing an unacceptably high risk of catastrophic uncontrolledcombustion.

Thus, there is a need to provide a method and system for the recovery ofheat from products of combustion that allows separate control of flowrates of hot oxygen to multiple burners from a single heat exchangerthat does not exhibit an unacceptably high risk of premature andpotential catastrophic failure.

In order to provide a practical method for heating oxygen with flue gas,the concept of using a heat transfer fluid was discussed by Illy et al.(International Glass Journal, 96, pp 65-72, 1998), for the case of aglass-melting furnace. For the sake of clarity, it should be noted thatIlly et al. refer to a heat exchanger in which the flue gas and oxidantare separated only by a wall as “direct”, whereas Chamberland et al.refer to it as “indirect”. Illy et al. discloses a scheme using threeheat exchangers: one to transfer heat from flue gas to a heat transferfluid, a second to transfer from the heated fluid to oxygen, and a thirdto transfer from the heated fluid air to natural gas fuel. According totheir description, the heat transfer fluid might be helium using aclosed loop recycling system, but could be any gas such as steam or air,with air being the least expensive option. Illy et al. did not considerhow hot oxygen flow would be controlled downstream of the heatexchangers.

One solution commercially implemented utilized, on a per burner basis,includes one heat exchanger for preheating oxygen and one heat exchangerfor preheating natural gas. The oxygen and natural gas are preheated inthe heat exchanger against a flow of hot air that is itself heatedagainst hot combustion gases in a recuperator. While this approach hasproduced desirable heat recoveries, the high number of heat exchangerscan drive up capital expense to an undesirably high level when the priceof metals suitable for oxygen service is itself high. Additionally, insmall to medium sized furnaces, the available space may not be adequatefor accommodating the large footprint taken up by the high number ofheat exchangers.

Thus, there is a need to provide a method and system of heat recoveryfrom products of combustion that does not produce an unacceptably highcapital expense or present an unsatisfactorily large footprint.

US 2007/0287107 discloses one solution to the problem of control ofoxygen flow when using hot oxygen. Two oxidants are delivered wherefirst is heated to at least 300° C. and the second is maintained at 200°C. or lower. The drawback of this method is that a substantial fractionof the oxygen flow is not significantly heated and thus the recovery ofheat from the flue gas is limited.

Thus, there is a need to provide a method and system of heat recoveryfrom products of combustion that achieves a satisfactorily high degreeof heat recovery.

Another solution is to use multiple heat exchangers, preferably one heatexchanger per burner, but at least one heat exchanger per 3 burners.This solution is described in US2010/0258263 and WO2008/141937. Thisapproach results in a very high capital expense because of the need tohave one heat exchanger for oxygen per 1-3 burners as well as one heatexchanger for fuel per 1-3 burners. Moreover, the large number of heatexchangers as a whole consumes a lot of space, as each heat exchanger israther large.

Thus, there is a need to provide a method and system of heat recoveryfrom products of combustion that does not require a very high capitalexpense and does not consume an undesirably high amount of space.

U.S. Pat. No. 6,250,916 discloses one solution where hot combustion gasis used to preheat air which is used, in turn, to preheat oxygen. In oneembodiment, and as best illustrated in FIG. 2, each one of severalburners B is associated with one heat exchanger HX_(O) for preheatingoxygen O_(C) and one heat exchanger HX_(F) for preheating fuel F_(C).The preheated oxygen O_(H) and preheated fuel F_(H) are combusted at theburners B to produce the hot combustion gases FG. Air A is heatexchanged with hot combustion gases FG at a recuperator R and directedin parallel to the heat exchangers HX_(O), HX_(F) as multiple streamsequal in number to the number of burners. Similar to US2010/0258263 andWO2008/141937, this approach also results in a very high capital expenseand consumes a lot of space.

In another embodiment of U.S. Pat. No. 6,250,916, and as bestillustrated in FIG. 3, air A is preheated with hot combustion gases FGat a recuperator R and directed through three heat exchangers HX_(O), inseries, for preheating oxygen O_(C). The preheated oxygen O_(H) fromeach heat exchanger HX_(O) is split into two lines each one of which isdirected to one of two burners B in a pair of burners B. The cooler airexiting the last heat exchanger HX_(O) for preheating oxygen O_(C) isthen directed through three heat exchangers HX_(F), again in series, forpreheating fuel F_(C). The preheated fuel F_(H) from each heat exchangerHX_(F) is split into two lines each one of which is directed to one oftwo burners B in a pair of burners B. Similar to US 2009/0084140, inorder to have separate control of the flow rate of oxygen for eachburner in a pair of burners, flow control devices must be locateddownstream of the heat exchangers, thereby subjecting them to hot oxygenattach and raising the potential for premature and potentialcatastrophic failure. While the oxygen flow rate for each burner in apair of burners may be fixed, and thereby significantly decrease theability to control heat flux within the furnace, the ratio of heatexchangers to burners is still as high as 1:2. Thus, this approach doesnot achieve a sufficiently desirable reduction in capital cost and spacerequirements.

Thus, there is a need to provide a method and system of heat recoveryfrom products of combustion that allows a greater degree of control overthe individual flow rates of burner oxygen without an unacceptably highrisk of premature and potentially catastrophic failure of the flow ratecontrol devices and without incurring an unacceptably high capitalexpense.

SUMMARY

There is provided a system for recovering heat from a furnace,comprising: a source of oxidant; a recuperator or regenerator; nburners, n being an integer greater than or equal to two, each of saidburners comprising a fuel nozzle and an oxidant nozzle; a heat exchangercomprising a housing having opposite feed and discharge ends, a hotfluid inlet and a cold fluid outlet fluidly communicating with aninterior of said housing, and a plurality of oxidant tubes, the feedinlet having n cold oxidant inlets, the discharge end having n hotoxidant outlets, the plurality of oxidant tubes comprising n sets ofoxidant tubes each set of which fluidly communicates between anassociated one of said n cold oxidant inlets and an associated one ofsaid n hot oxidant outlets; a hot heat exchange fluid conduit having afirst end connected to and receiving a hot heat exchange fluid from saidrecuperator or regenerator and a second end fluidly communicating withsaid hot fluid inlet; n cold oxidant feed conduits each one of which hasfirst and second ends, each of said cold oxidant feed conduit first endsfluidly communicating with said oxidant source, each one of said coldoxidant feed conduit second ends fluidly communicating with a respectiveone of said cold oxidant inlets; n cold oxidant flow control deviceseach one of which is disposed in a respective one of said n cold oxidantfeed conduits, flows of oxidant through said n cold oxidant feedconduits being separately and independently controllable by saidcorresponding cold oxidant flow control devices; and n hot oxidant feedconduits each one of which has first and second ends, each one of saidhot oxidant feed conduit first ends fluidly communicating with arespective one of said hot oxidant outlets, each one of said hot oxidantfeed conduit second ends fluidly communicating with a respective one ofsaid burners.

There is also provided a method recovering heat from a furnace,comprising the following steps. A heat transfer fluid is heated at aregenerator or recuperator through heat exchange with hot combustiongases to produce a hot heat transfer fluid. N flows of cold oxidant areflowed from an oxidant source to a heat exchanger, said heat exchangercomprising a housing, a plurality of oxidant tubes comprising n sets ofoxidant tubes, each set extending through an interior of the housing andfluidly communicating between a respective one of said cold oxidantinlets formed in the housing and a respective one of said hot oxidantoutlets formed in the housing, a hot heat exchange fluid inlet fluidlycommunicating with an interior of the housing, and a hot fluid outletfluidly communicating with the housing interior, each of said n flows ofcold oxidants being directed into a respective one of said sets ofoxidant tubes, n being an integer equal to or greater than 2. The hotheat transfer fluid is flowed to said hot heat exchange fluid inlet.Heat is exchanged between the hot heat transfer fluid and said flows ofcold oxidant at said heat exchanger to produce n flows of hot oxidant atsaid hot oxidant outlets and a flow of cooled heat transfer fluid. Saidflows of hot oxidant are flowed from said hot oxidant outlets to nburners, each burner comprising an oxidant nozzle and a fuel nozzle.Fuel and said hot oxidant are combusted at said burners to produce thehot combustion gases, wherein flow rates of said flows of cold oxidantmay controlled independent of one another with a respective n oxidantflow control devices disposed upstream of said heat exchanger.

There is also provided a system for recovering heat from a furnace,comprising: a source of oxidant having an oxygen concentration greaterthan that of air; a recuperator or regenerator, said recuperator orregenerator adapted and configured to exchange heat between a flow ofcool shell-side fluid and a flow of hot combustion gases from a furnaceto produce a flow of hot shell-side fluid; a first shell and tube heatexchanger; a first shell and tube heat exchanger; first and second cooloxidant feed conduits; a first controller; and first and second hotoxidant feed conduits. The first shell and tube heat exchangercomprises: a shell, a hot shell-side fluid inlet and a cool shell-sidefluid outlet formed in the shell thereof, first and second oxidantinlets receiving first and second main flows of oxidant, respectively,first and second sets of one or more oxidant tubes each, the first andsecond sets receiving the first and second main flows of oxidant,respectively, from the first and second oxidant inlets, each of theoxidant tubes extending through an interior of the shell, and first andsecond oxidant outlets receiving the first and second main flows ofoxidant, respectively, from the first and second sets of oxidant tubes,respectively. The first shell and tube heat exchanger is adapted andconfigured to transfer heat from the flow of hot shell-side fluid to themain flows of oxidant flowing through the oxidant tubes. The first cooloxidant feed conduit fluidly communicates between the source of oxidantand the first oxidant inlet. The second cool oxidant feed conduitfluidly communicates between the source of oxidant and the secondoxidant inlet. The first and second oxidant flow control devices aredisposed in the first and second cool oxidant feed conduits,respectively. The first controller is adapted and configured to controlflow rates of oxidant from the oxidant source and through the first andsecond cool oxidant feed conduits with the first and second oxidant flowcontrol devices, respectively. Each of the first and second oxidantflows through the cool oxidant feed conduits may be controlled by saidfirst controller independently and separately from control of one other.The first and second hot oxidant feed conduits receive the first andsecond main oxidant flows, respectively, from the first and secondoxidant outlets, respectively.

There is also provided a charge heating installation utilizingpre-heated oxidant, comprising: the above-recited system for recoveringheat from a furnace; first and second burners receiving first and secondflows of hot oxidant, respectively, from the first and hot oxidant feedconduits, respectively; and a melting furnace containing a charge. Eachof the burners is operatively associated with the furnace such that thecharge is heated through combustion of a fuel and the hot oxidantinjected by the burners. The recuperator or regenerator receives a flowof hot combustion gases from the combustion of the hot oxidant and fuelin the furnace to produce the flow of hot shell-side fluid.

There is also provided another method for recovering heat from afurnace. The method comprises the following steps. Fuel and a first flowof hot oxidant are injected from a first burner, the hot oxidant havingan oxygen concentration higher than that of air. Fuel and a second flowof hot oxidant are injected from a second burner. The injected fuel andhot oxidant are combusted to heat a charge in the furnace and producehot combustion gases. Heat is exchanged with a recuperator orregenerator between a flow of cool shell-side fluid and a flow of thehot combustion gases to produce a flow of hot shell-side fluid. Firstand second main flows of oxidant are heated through heat exchange at ashell and tube heat exchanger with the hot shell-side fluid to producethe first and second flows of hot oxidant. Flow rates of first andsecond flows of oxidant flowing in first and second cool oxidant feedconduits upstream of the oxidant inlets are independently and separatelycontrolled, wherein the first and second main flows of oxidant areobtained from the first and second flows of oxidant.

Any one or more of the above disclosed systems, installation, or methodsmay include one or more of the following aspects:

-   -   the flow of cooled heat transfer fluid is collected at a cold        fluid outlet fluidly communicating with an interior of the        housing and directed back to said recuperator or regenerator to        complete a cycle of heat transfer.    -   the heat transfer fluid is air, carbon dioxide, helium, other        inert gas, or mixtures thereof.    -   heat conducting packing is present inside the housing and is in        thermal contact between adjacent oxidant tubes.    -   the packing is a ceramic material.    -   each of said cold oxidant flows is split into an interior stream        which is directed into said oxidant tubes and an exterior        streams which is directed outside of said heat exchanger, the        exterior streams being recombined with the corresponding        interior streams to provide said hot oxidant flows, the degree        to which each cold oxidant flow is split between the respective        interior stream and the respective exterior stream is controlled        independently from other of said cold oxidant flows with an        associated n hot oxidant flow control devices.    -   each split of the cold oxidant flows is controlled independently        of other of said cold oxidant flows based upon a temperature        sensed in the associated hot oxidant feed conduit downstream of        said recombination.    -   the cooled heat exchange fluid is collected at a cold fluid        outlet fluidly communicating with an interior of said housing.    -   before said recombination, said exterior streams are heated        through heat exchange against said cooled heat exchange fluid at        an additional heat exchanger.    -   n is four or greater    -   the furnace is a glass furnace.    -   none of the first and second oxidant flows bypass the heat        exchanger so that the first and second oxidant flows become the        first and second main oxidant flows, respectively.    -   first and second bypass valves are disposed in the first and        second cool oxidant feed conduits.    -   each of the bypass valves is adapted and configured to split an        associated one of the oxidant flows into first and second        portions.    -   the first portion split by the first bypass valve being the        first main oxidant flow and the second portion split by the        first bypass valve being a first bypass oxidant flow.    -   the first portion split by the second bypass valve being the        second main oxidant flow and the second portion split by the        second bypass valve being a second bypass oxidant flow.    -   the first and second bypass flows flowing through first and        second bypass flow conduits disposed entirely outside the shell.    -   the first hot oxidant feed conduit receiving the first bypass        flow from the first bypass flow conduit at which the first        bypass flow is combined with the first main oxidant flow.    -   the second hot oxidant feed conduit receiving the second bypass        flow from the second bypass flow conduit at which the second        bypass flow is combined with the second main oxidant flow.    -   each of the splits of the first and second oxidant flows into        the respective first and second portions is controlled by the        controller separately and independently of one another.    -   It further comprises a source of gaseous fuel and second shell        and tube heat, a first cool fuel feed conduit; a second cool        fuel feed conduit; first and second fuel flow control devices        disposed in the first and second cool fuel feed conduits; and        first and hot fuel feed conduits, The second shell and tube heat        exchanger comprises:        -   a shell,        -   a hot shell-side fluid inlet and a cool shell-side fluid            outlet formed in the shell thereof,        -   first and second fuel inlets receiving first and second main            flows of fuel, respectively,        -   first and second sets of one or more fuel tubes each, the            first and second sets of fuel tubes receiving the first and            second main flows of fuel, respectively, from the first and            second fuel inlets, each of the fuel tubes extending through            an interior of the shell, and        -   first and second fuel outlets receiving the first and second            main flows of fuel, respectively, from the first and second            sets of fuel tubes, respectively, the second shell and tube            heat exchanger being adapted and configured to transfer heat            from the flow of hot shell-side fluid to the main flows of            fuel flowing through the fuel tubes.    -   The first cool fuel feed conduit fluidly communicates between        the source of fuel and the first fuel inlet. The second cool        fuel feed conduit fluidly communicates between the source of        fuel and the second fuel inlet. The first controller or a second        controller is adapted and configured to control flow rates of        fuel from the fuel source and through the first and second cool        fuel feed conduits with the first and second fuel flow control        devices, respectively. Each of the first and second fuel flows        through the cool fuel feed conduits may be controlled by said        controller independently and separately from control of one        other. The first and hot fuel feed conduits receive the first        and second main fuel flows, respectively, from the first and        second fuel outlets, respectively.    -   the shell-side fluid is air, carbon dioxide, helium, nitrogen,        other inert gas, or mixtures thereof.    -   the cool shell-side fluid is produced through heat exchange        between the hot shell-side fluid and the first and second main        flows of oxidant at the shell and tube heat exchanger.    -   Each of the first and second oxidant flows is split into first        and second portions with first and second bypass valves,        respectively. The first portion split by the first bypass valve        is the first main oxidant flow and the second portion split by        the first bypass valve is a first bypass oxidant flow. The first        portion split by the second bypass valve is the second main        oxidant flow and the second portion split by the second bypass        valve is a second bypass oxidant flow. The first and second        bypass flows flow through first and second bypass flow conduits        disposed entirely outside the shell. The first bypass flow is        combined with the first main oxidant flow downstream of the        shell and tube heat exchanger. The second bypass flow is        combined with the second main oxidant flow downstream of the        shell and tube heat exchanger.    -   each of the splits of the first and second oxidant flows into        the respective first and second portions is controlled by the        controller separately and independently of one another.    -   The overall design of the heat exchanger is optimized based upon        the total power of the combined burners receiving pre-heated        oxidant. This means that the diameter of the oxidant tubes, the        number of oxidant tubes, the oxidant tube pitch (i.e., the tube        to tube spacing), and the oxidant tube length to diameter ratio        are optimized based upon the total combined power of the burners        receiving the pre-heated fuel. Once these variables are        optimized, the heat exchanger is provided with a single shell.        Then, the fuel tubes are divided into sets based upon the number        of fuel streams to be pre-heated by the heat exchanger where        each set receives a separate fuel stream. This design        optimization can be distinguished from a combination of heat        exchangers each one of which has been individually optimized        based upon the burners it supplies with pre-heated fuel where        the combination includes a number of shells equal to the number        of heat exchangers combined. A combination of heat exchangers is        less efficient than the optimized heat exchanger of the        invention.    -   the heat exchanger is provided with a single shell.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 is a schematic of one prior art heat recovery solution in afurnace.

FIG. 2 is a schematic of another prior art heat recovery solution in afurnace.

FIG. 3 is a schematic of yet another prior art heat recovery solution ina furnace.

FIG. 4 is a schematic of a non-limiting example of heat recovery in afurnace involving one oxidant heat exchanger and one fuel heat exchangerfor every four burners.

FIG. 5 is a schematic of a non-limiting example of heat recovery in afurnace involving one fuel heat exchanger for every four burners.

FIG. 6 is a schematic of a non-limiting example of heat recovery in afurnace including one oxidant heat exchanger and one fuel heat exchangerfor every four burners.

FIG. 7A is a schematic elevation side view of a non-limiting example ofa shell and tube heat exchanger.

FIG. 7B is a schematic elevation side view of the heat exchanger of FIG.7A from a point of view rotated 90° from the point of view of FIG. 7A.

FIG. 7C is a schematic elevation end view of the heat exchanger of FIG.7A.

FIG. 7D is a cross-sectional end view of the heat exchanger of FIG. 7Ataken along the line I-I.

FIG. 7E is a cross-sectional end view of the heat exchanger of FIG. 7Ataken along the line II-II.

FIG. 7F is a cross-sectional side view of the heat exchanger of FIG. 7Ataken along the line III-III.

FIG. 7G is an alternative cross-sectional side view of the heatexchanger of FIG. 7A taken along the line III-III illustrating featuresnot present in FIG. 7F.

FIG. 8 is a process flow diagram of a bypass scheme for controlling thetemperature of one of the oxidant streams downstream of the heatexchanger.

FIG. 9 is a process flow diagram of the invention.

FIG. 10 is a process flow diagram of a single source of oxidant splitinto multiple streams.

DETAILED DESCRIPTION

In conventional furnaces, a single source of oxidant and a single sourceof fuel are typically split up into multiple streams (at ambienttemperature) for injection by multiple burners. If an operator wishes tocontrol the power of a particular burner or burners independently of thepowers of other burners, it is relatively simple matter of adjusting theflow rate of the fuel and/or oxidant for the burner(s) at issue using aflow control device upstream of or at the burner level.

In the cases of a conventional furnace including burners usingpre-heated oxidant and/or pre-heated fuel, each of the reactants (fueland oxidant) is directed to a heat exchanger as a single stream at whichit is heated through heat exchange with a hot fluid. The heatedreactant(s) is then split up into multiple streams in parallel forinjection by multiple burners. If an operator wishes to control thepower of an individual burner or burners independently of the powers ofother burners, the flow rate of the fuel and/or oxidant for theburner(s) at issue hypothetically could be adjusted using a flow controldevice(s) in the line(s) split off from the pre-heated oxidant streamand/or line(s) split off from the pre-heated fuel stream.

However, this hypothetical approach suffers three significantdisadvantages. First, the tolerances in between the internal componentsof the flow control device are increased due to thermal expansion ofthose components caused by heat transfer from the hot reactant to thosecomponents. The increased tolerances result in the formation of leaksfrom the device and thus poor control over the flow rate if not creationof a safety risk. Second, any change in the flow rate of a single one ofthe multiple streams will affect the pressures in the lines conveyingthe other of the streams because those lines are in parallel and are inflow communication with one another. This effect is exacerbated by thefact that the preheated reactant is at a higher pressure after heatingthan the ambient temperature reactant. Because the flow rates in theother lines are subject to significant pressure variations and must besimultaneously controlled, this leads to a very complex and difficultcontrol scheme. Third and in the case of hot oxidant in particular, hotoxidative attack of internal components of the flow control device cancause premature or even catastrophic failure due to the enhancedreaction rate of oxidation of the material comprising the device.

The invention overcomes these disadvantages by: a) splitting up thereactant, upstream of heating, into multiple streams, b) using a novelheat exchanger, and c) controlling the flow rates of the reactantstreams with flow control devices disposed upstream of the heatexchanger. The flow control devices are not subjected to heating andthus remain relatively leak-proof because the tolerances in between theinternal components are not affected. Because the pressure of thereactant source (oxidant or fuel) is at a much higher pressure thanthose of the multiple reactant streams upstream of the heat exchanger,an adjustment of the flow rate of one of the streams upstream of theheat exchanger does not make as significant an impact in the pressure inthe other of the streams. Thus, there is longer a need to simultaneouslycontrol the flow rates of the other streams, or alternatively, suchsimultaneous control is more easily done due to the relatively smallerpressure variations at ambient temperature.

In general, the system and method includes a recuperator or regeneratorthat is used to transfer heat from hot combustion gases produced in afurnace (containing a charge) to a heat transfer fluid. A shell and tubeheat exchanger is used to transfer heat from the hot heat transfer fluidto multiple oxidant streams and/or multiple natural gas streams. Theheat transfer fluid is called the shell-side fluid because it flowsthrough an interior of the heat exchanger on the shell-side, i.e., inthe space between the interior surface of the shell and the exteriorsurfaces of tubes extending in the space. Hence, the oxidant or fuel iscalled the tube-side fluid because it flows on the tube-side (i.e.,through tubes extending through the heat exchanger. As best illustratedin FIG. 9, control devices D_(A), D_(B), D_(C), D_(D) equal in number tothe number of oxidant and/or fuel streams M1 _(A), M1 _(B), M1 _(C), M1_(D) are disposed upstream of the heat exchanger HE and are used tocontrol the flow rates of the oxidant and/or fuel streams M1 _(A), M1_(B), M1 _(C), M1 _(D) flowing to the heat exchanger HE. These flowcontrol devices D_(A), D_(B), D_(C), D_(D) are controlled with acontroller C separately and independently of one another. This meansthat adjustment of the flow rate of one of the oxidant (or fuel) streamsM1 _(A), M1 _(B), M1 _(C), M1 _(D) does not require concomitantadjustment of the flow rates of the other of the oxidant (or fuel)streams.

As best illustrated in FIG. 10, a single source of oxidant M is split upinto multiple streams of oxidant M1 _(A), M1 _(B), M1 _(C), M1 _(D). Theshell and tube heat exchanger HE includes multiple oxidant (or fuel)inlets and outlets equal in number to the number of oxidant (or fuel)streams M1 _(A), M1 _(B), M1 _(C), M1 _(D) being pre-heated. Extendingin flow communication between an associated inlet and outlet is a set oftubes termed oxidant tubes in the case of oxidant pre-heating or fueltubes in the case of fuel pre-heating. Each oxidant (or fuel) stream isfirst received by an oxidant (or fuel) inlet and divided into aplurality of sub-streams that flow through the tubes of the associatedset. Typically, the tubes extend between upstream and downstream tubesheets in order to separate the oxidant or fuel from the hot shell-sidefluid. The sub-streams of oxidant (or fuel) for a given set of tubes arethen recombined into the thus-heated flow of oxidant (or fuel) whichflows out of the heat exchanger HE at an associated oxidant (or fuel)outlet. Thus, it is seen that each flow of oxidant (or fuel) to bepre-heated is associated with one of the oxidant (or fuel) inlets, withone of the sets of oxidant (or fuel) tubes, and one of the oxidant (orfuel) outlets. The number of tubes per set is non-limiting and may beselected based upon space, design, and material limitations. Typically,the number of tubes per set ranges from 2-12.

The shell and tube heat exchanger HE may optionally include conventionalbaffles oriented perpendicular to, and outside of, the oxidant (or fuel)tubes so that the hot shell-side fluid follows a serpentine path thatallows heat transfer between the hot shell-side fluid and a firstportion of the oxidant (or fuel) tubes, then with second portions of theoxidant (or fuel) tubes adjacent to the first portions, and so on. Inthis manner, the hot shell-side fluid acts to equalize the temperaturesof the oxidant (or fuel) tubes, and therefore equalize the temperaturesof the oxidant (or fuel) flowing through the tubes. The shell and tubeheat exchanger HE may have a cross-sectional configurationconventionally used in the heat exchanger art, including but not limitedto: circular, oval, rectangular, and square.

While the heat exchanger HE may be made of out of a wide variety ofmaterials, typically it is made of a material that is recognized asbeing suitable for handling hot oxidants (in the case of oxygenpre-heating) or hot gaseous fuels (in the case of fuel pre-heating).Additionally, each set of oxidant (or fuel) tubes may optionally beseparated from one another by walls running parallel to the tubes. Inthis case, the hot shell-side fluid is split into a plurality ofsub-streams equal in number to the number of sets where each singlesub-stream of hot shell-side fluid is caused to flow alongside only oneset of oxidant (or fuel) tubes.

The oxidant has an oxygen concentration higher than that of air.Typically, it is oxygen-enriched air or industrially pure oxygen. In thecase of no fuel pre-heating, the fuel may be any fuel conventionallyused in burners associated with furnaces for heating a charge, includingpulverent, particulate, or crushed solid fuels, liquid fuels, or gaseousfuels. In the case of fuel pre-heating, the fuel is gaseous. Typically,the fuel is natural gas, methane, or propane. The furnace may be anyconventional furnace designed for heating and/or melting a charge, suchas ceramic, glass, or metal. Typically, it is a melting furnace, such asa glass melting furnace. The shell-side fluid may be air, carbondioxide, helium, other inert gas, or mixtures thereof.

The burner may be any burner suitable for the combustion of a fuel withan oxidant in a furnace for heating and/or melting a charge (such asmetal or glass), for example, those disclosed by U.S. Pat. No.6,910,879, US 2007-0172781, and US 2007-0281254.

In operation, the ratio of the flow rate of shell-side fluid to the flowrate of the oxidant stream or fuel stream is dependent in a trivial wayupon a variety of factors, including the type of shell-side fluid, thetype of oxidant, the temperature of the shell-side fluid, thetemperature of the oxidant before pre-heated, the temperature of thefuel before pre-heating, the desired hot oxidant and hot fueltemperatures, process requirements, and the particular configuration ofthe heat exchanger. Typically, the ratio is at least 2:1.

The temperature of the shell-side fluid and the hot combustion gases arealso dependent in a trivial way upon a variety of factors, including thetype of shell-side fluid, the type of combustion gases, the temperatureof the shell-side fluid before heat exchange at the recuperator orregenerator, the temperature of the hot combustion gases, processrequirements, and the particular configuration of the recuperator orregenerator. While higher temperatures are possible, typically the hotshell-side fluid is at a temperature up to about 730° C. Typically, theoxidant and fuel before pre-heating are at ambient temperature. Afterpre-heating, the oxidant is typically at a temperature of up to about700° C., but higher temperatures are still possible. After pre-heating,the fuel is typically at a temperature of up to about 450° C. After heatexchange between the hot shell-side fluid and the oxidant and fuelstreams, the cooled shell-side fluid is typically at a temperature ofabout 200-300° C.

Optionally, each of the oxidant streams is pre-heated at a first heatexchanger while each of the fuel streams is pre-heated at a second heatexchanger. The flow of hot shell-side fluid may be arranged in parallelwhereby two streams of the hot shell-side fluid are directed to the twoheat exchangers. The flow hot shell-side fluid may instead be arrangedin series whereby one of the oxidant and fuel streams is pre-heated atthe first heat exchanger through heat exchange with the hot shell-sidefluid, and the now-somewhat cooled hot shell-side fluid exiting thefirst heat exchanger is used to pre-heat the other of the oxidant andfuel streams at the second heat exchanger.

Optionally, the shell-side fluid may be recirculated. Recirculated meansthat after heat exchange is performed between the shell-side fluid andthe oxidant and/or fuel streams, it is returned to the regenerator orrecuperator to complete a circuit. In this case, shell-side fluids otherthan air become more cost-effective. The shell-side fluid may be chosenso as to optimize heat transfer between conduits, for example, bychoosing a fluid of high thermal conductivity such as helium.Alternatively, overall heat transfer may be optimized by choosing afluid of high heat capacity such as carbon dioxide. Optionally, theshell-side fluid is any other inert gas or mixtures of any of helium,carbon dioxide, and the other inert gas.

The overall design of the heat exchanger HE is optimized based upon thetotal power of the combined burners receiving pre-heated oxidant (and/orfuel). This means that the diameter of the oxidant (or fuel) tubes, thenumber of oxidant (or fuel) tubes, the oxidant (or fuel) tube pitch(i.e., the tube to tube spacing), and the oxidant (or fuel) tube lengthto diameter ratio are optimized based upon the total combined power ofthe burners receiving the pre-heated oxidant (or fuel). Once thesevariables are optimized, the heat exchanger is provided with a singleshell. Then, the oxidant (or fuel) tubes are divided into sets basedupon the number of oxidant (or fuel) streams to be pre-heated by theheat exchanger where each set receives a separate oxidant (or fuel)stream. This design optimization can be distinguished from a combinationof heat exchangers each one of which has been individually optimizedbased upon the burners it supplies with pre-heated oxidant or fuel wherethe combination includes a number of shells equal to the number of heatexchangers combined. A combination of heat exchangers is less efficientthan the optimized heat exchanger of the invention.

The flow rate of each individual, separately controlled, oxidant (orfuel) stream M1 _(A), M1 _(B), M1 _(C), M1 _(D) is typically varied overtime in response to process requirements. If the flow rate of one orless than all of the oxidant (or fuel) streams M1 _(A), M1 _(B), M1_(C), M1 _(D) is lowered, the slower oxidant (or fuel) stream flow ratecauses that slower-rate stream to be heated to a relatively highertemperature than other faster-rate streams. This is because the longerresidence time of the oxidant (or fuel) inside the heat exchanger HEallows greater heat transfer between the hot heat transfer fluid to theslower-rate stream. Conversely, a higher oxidant (or fuel) stream flowrate causes that faster-rate stream to be heated to a relatively lowertemperature than other slower-rate streams because of the shorterresidence time of the faster rate stream.

Because the individual oxidant (or fuel) streams M1 _(A), M1 _(B), M1_(C), M1 _(D) may have higher or lower flow rates (and therefore theoxidant (or fuel) tubes have correspondingly lower or highertemperatures), the thermal expansion or thermal contraction of eachoxidant (or fuel) tube conveying that higher or lower flow rate streammay be greater or lesser than those of the other oxidant (or fuel)streams. In order to avoid the possibility that the differing thermalexpansions and/or contractions may place undue stresses on the oxidant(or fuel) tubes and the shell, each set of oxidant (or fuel) tubes maybe provided with a separate thermal expansion joint. In this manner, theseparate joints may allow the differing expansions and contractions ofthe different sets of tubes without subjecting the heat exchanger HE toundue stresses.

It is desirable to maintain the oxidant (or fuel) temperatures of thevarious pre-heated oxidant (or fuel) streams as close as possible.However, and as discussed above, when individual oxidant (or fuel)streams have higher or lower flow rates, their temperatures may be loweror higher than the other lower or higher flow rate streams. There areseveral ways to compensate for these different temperatures.

Under one approach and where appropriate, thermally conductive packingmaterials may be used to facilitate heat transfer, for example aluminapacking may be used. When using packing materials, it is important tohave a sufficiently loose packing so that the pressure drop isminimized, while still achieving good thermal contact with the hot andcold surfaces of the heat exchanger. Also, thermal conduction betweenthe oxidant (or fuel) streams is maximized, for example, by usingthermally conductive plates to connect the oxidant (or fuel) tubes toone another. Thus heat transfer occurs between streams via the plates.By facilitating heat transfer from tube to tube, differences intemperature between the various oxidant (or fuel) streams may becompensated for.

Under another approach, the oxidant (or fuel) tubes of a given set ofoxidant (or fuel) tubes are not disposed alongside one another asdescribed above. Thus, after division of a given oxidant (or fuel)stream into a plurality of sub-streams, the oxidant (or fuel) tubes forthe various oxidant (or fuel) streams are interleaved with one another.For example and in the case of three streams of oxidant (or fuel) eachone of which is divided amongst three oxidant (or fuel) tubes, a firsttube of the first stream extends alongside the first tube of the secondstream which in turn extends alongside the first tube of the thirdstream. A second tube of the first stream extends alongside the secondtube of the second stream which in turn extends alongside the secondtube of the third stream. Finally, a third tube of the first streamextends alongside the third tube of the second stream which in turnextends alongside the third tube of the third stream. In each case, thecorresponding first tubes (of the first, second, and third streams) arecloser to one other than they are to the second tubes or third tubes ofthe set stream.

Under yet another approach and as best illustrated by FIG. 8, one ormore flows of oxidant (or fuel) M1 _(A), M1 _(B), M1 _(C), M1 _(D) aresplit into a main flow M2 _(A), M2 _(B), M2 _(C), M2 _(D) and a bypassflow M3 _(A), M3 _(B), M3 _(C), M3 _(D) with a control valve V_(A),V_(B), V_(C), V_(D). The main flow M2 _(A), M2 _(B), M2 _(C), M2 _(D) isdirected into the heat exchanger HE where it is heated through heatexchange with the hot shell-side fluid. The bypass flow M3 _(A), M3_(B), M3 _(C), M3 _(D) completely bypasses the heat exchanger HE and isrecombined with the now-heated main flow. A controller C controls theratio of the main M2 _(A), M2 _(B), M2 _(C), M2 _(D) and bypass flow M3_(A), M3 _(B), M3 _(C), M3 _(D) rates via the control valve V1 _(A), V1_(B), V1 _(C), V1 _(D) to a value within the range of 1:0 to 0:1.Typically, the value is in the range of 9:1 to 7:3. While any knownprocess control scheme may be utilized to control this ratio, generallyspeaking, when a temperature of the stream (downstream of where the mainflow M2 _(A), M2 _(B), M2 _(C), M2 _(D) and bypass flows M3 _(A), M3_(B), M3 _(C), M3 _(D) are recombined) exceeds a set maximumtemperature, the controller C commands the control valve V1 _(A), V1_(B), V1 _(C), V1 _(D) to increase the bypass flow rate and decrease themain flow rate. When a temperature of the stream (again, downstream ofwhere the main and bypass flows are recombined) goes below a set minimumtemperature, the controller C commands the control valve V1 _(A), V1_(B), V1 _(C), V1 _(D) to decrease the bypass flow rate and increase themain flow rate.

The overall flow M1 _(A), M1 _(B), M1 _(C), M1 _(D) of cold oxidant issplit between an associated main flows M2 _(A), M2 _(B), M2 _(C), M2_(D) and bypass flows M3 _(A), M3 _(B), M3 _(C), M3 _(D). The bypassflow M3 _(A), M3 _(B), M3 _(C), M3 _(D) is directed to the feed end ofthe heat exchanger HE, heated in the oxidant tubes in heat exchange withthe hot heat transfer fluid, and discharged out the hot oxidant outlet.The bypass flow M1 _(A), M1 _(B), M1 _(C), M1 _(D) remains outside theheat exchanger HE and is recombined with the main flow M2 _(A), M2 _(B),M2 _(C), M2 _(D) to again provide the overall flow. A temperaturesetpoint is predetermined for the recombined flow of hot oxidant. Bymeasuring the temperatures of the combined flow of M2 _(A) and M3 _(A)(at T_(A)), the combined flow of M2 _(B) and M3 _(B) (at T_(B)), thecombined flow of M2 _(C) and M3 _(C) (at T_(C)), and the combined flowof M2 _(D) and M3 _(D) (at T_(D)), and adjusting the allocation of theoverall flow M1 _(A), M1 _(B), M1 _(C), M1 _(D) into main M2 _(A), M2_(B), M2 _(C), M2 _(D) and bypass flows M3 _(A), M3 _(B), M3 _(C), M3_(D), the temperatures of the hot oxidant after the afore-mentionedrecombination of the streams may be controlled. In other words, if theone or more temperatures of the aforementioned recombined flows ishigher than the setpoint temperature, M3 _(A), M3 _(B), M3 _(C), M3 _(D)is increased and M2 _(A), M2 _(B), M2 _(C), M2 _(D) is decreased at avalve V_(A), V_(B), V_(C), V_(D) accomplishing the split until thetemperature(s) of the aforementioned recombined flow(s) reaches thesetpoint. Preferably, a butterfly valve is used to do this. Thetemperature(s) of the aforementioned recombined flow(s) will increase asM1 _(A), M1 _(B), M1 _(C), M1 _(D) decreases and will eventuallyapproach a limit close to the hot heat transfer fluid temperature. Closeto this limit, those temperatures will increase slowly as M1 _(A), M1_(B), M1 _(C), M1 _(D) decreases. On the other hand, those temperatureswill decrease through dilution of the main flow M2 _(A), M2 _(B), M2_(C), M2 _(D) with the cold, unheated bypass flow M3 _(A), M3 _(B), M3_(C), M3 _(D). This temperature decrease is more rapid close to thelimit. In this way, we can achieve a desirable temperature irrespectiveof overall flow rates.

One generalized and illustrative arrangement of the invention is shownin FIG. 4. Hot combustion gases 1 preheat a heat transfer fluid (i.e.,the shell-side fluid) 3 at a recuperator or regenerator 5. The resultanthot shell-side fluid 7 flows to a heat exchanger 9 for preheatingoxidant where it exchanges heat with flows of cold oxidant 11 _(A), 11_(B), 11 _(C), 11 _(D). The resultant flows of hot oxidant 13 _(A), 13_(B), 13 _(C), 13 _(D) are directed to burners 23 _(A), 23 _(B), 23_(C), 23 _(D). The flows of fuel 19 _(A), 19 _(B), 19 _(C), 19 _(D) aredirected to the burners 23 _(A), 23 _(B), 23 _(C), 23 _(D) where thefuel combusts with the hot oxidant to produce the hot combustion gases1. The hot shell-side fluid is cooled at heat exchanger 9 and isoptionally recirculated to the recuperator or regenerator 5 as theshell-side fluid 3 to complete a loop.

Another generalized and illustrative arrangement of the invention isshown in FIG. 5. Hot combustion gases 1 preheat the shell-side fluid 3at a recuperator or regenerator 5. The resultant hot shell-side fluid 7flows to a heat exchanger 17 for preheating fuel where it exchanges heatwith flows of cold fuel 19 _(A), 19 _(B), 19 _(C), 19 _(D). Theresultant flows of hot fuel 21 _(A), 21 _(B), 21 _(C), 21 _(D) aredirected to the burners 23 _(A), 23 _(B), 23 _(C), 23 _(D) where the hotfuel combusts with the flows of oxidant 11 _(A), 11 _(B), 11 _(C), 11_(D). The hot shell-side fluid is cooled at heat exchanger 17 and isoptionally recirculated to the recuperator or regenerator 5 as theshell-side fluid 3 to complete a loop.

Another generalized and illustrative arrangement of the invention isshown in FIG. 6. Hot combustion gases 1 preheat the shell-side fluid 3at a recuperator or regenerator 5. The resultant hot shell-side fluid 7flows to a heat exchanger 9 for preheating oxidant where it exchangesheat with flows of cold oxidant 11 _(A), 11 _(B), 11 _(C), 11 _(D). Theresultant flows of hot oxidant 13 _(A), 13 _(B), 13 _(C), 13 _(D) aredirected to burners 23 _(A), 23 _(B), 23 _(C), 23 _(D). The hotshell-side fluid is cooled at heat exchanger 9 and is directed to a heatexchanger 17 for preheating fuel where it exchanges heat with flows ofcold fuel 19 _(A), 19 _(B), 19 _(C), 19 _(D). The resultant flows of hotfuel 21 _(A), 21 _(B), 21 _(C), 21 _(D) are directed to the burners 23_(A), 23 _(B), 23 _(C), 23 _(D) where the hot fuel combusts with the hotoxidant to produce the hot combustion gases 1. Optionally, theshell-side fluid 3 (before heating at the recuperator or regenerator 5)may be the cooled shell-side fluid after heat exchanger with the heatexchanger 17.

While FIGS. 4-6 illustrate one heat exchanger for every four streams ofoxidant 11 _(A), 11 _(B), 11 _(C), 11 _(D) and one heat exchanger forevery four streams of fuel 19 _(A), 19 _(B), 19 _(C), 19 _(D), theinvention is not limited in such a manner. Rather, each heat exchangermay handle as few as two or three oxidant streams 11 _(A), 11 _(B), 11_(C), 11 _(D) or fuel streams 19 _(A), 19 _(B), 19 _(C), 19 _(D) or itmay handle more than four. Also, while FIGS. 4-6 illustrate only fourburners, there may be as few as two or three or as many as severaldozen. In the case of a glass melting furnace, typically all of theburners (utilizing pre-heated oxidant and/or fuel) on one side of afurnace receive pre-heated oxidant and pre-heated fuel from a pair ofheat exchangers (one of oxidant and one for fuel) while all of theburners on the opposite side receive pre-heated oxidant and pre-heatedfuel from a different pair of heat exchangers (again, one for oxidantand one for fuel). Also, while FIG. 6 illustrates pre-heating of theoxidant before the shell-side fluid 3 is used to pre-heat the fuel, thisorder may be reversed.

A non-limiting example of a shell and tube exchanger for use in theinvention is best shown in FIG. 7A-F, the flows of cold oxidant 11A,11B, 11C, 11D are received in respective oxidant channels/nozzles 33_(A), 33 _(B), 33 _(C), 33 _(D) formed in shell 36. The hot flows ofoxidant 13 _(A), 13 _(B), 13 _(C), 13 _(D) exit the heat exchanger fromrespective oxidant channels/nozzles 51 _(A), 51 _(B), 51 _(C), 51 _(D)also formed in shell 36. The flow of hot shell-side fluid 7 is directedinto an interior of the shell 36 via hot fluid inlet 35. The cooledshell-side fluid exits the heat exchanger from cold fluid outlet 37.

The interior spaces 41 _(A), 41 _(B), 41 _(C), 41 _(D) of the housingadjacent the oxidant (or fuel) channels/nozzles 33 _(A), 33 _(B), 33_(C), 33 _(D) are divided by dividers 39 to keep the flows of oxidant(or fuel) 13 _(A), 13 _(B), 13 _(C), 13 _(D) (21 _(A), 21 _(B), 21 _(C),21 _(D)) separate from one another. The interior spaces 49 _(A), 49_(B), 49 _(C), 49 _(D) adjacent the oxidant (or fuel) channels/nozzles51 _(A), 51 _(B), 51 _(C), 51 _(D) are similarly divided by dividers 59to keep the flows of hot oxidant (or fuel) 13 _(A), 13 _(B), 13 _(C), 13_(D) (21 _(A), 21 _(B), 21 _(C), 21 _(D)) separate from one another.

Each flow of oxidant (or fuel) 13 _(A), 13 _(B), 13 _(C), 13 _(D) (21_(A), 21 _(B), 21 _(C), 21 _(D)) is split into a plurality ofsub-streams that flow from a corresponding chamber 41 _(A), 41 _(B), 41_(C), 41 _(D) and into a corresponding set of oxidant tubes (or fuel) 45_(A), 45 _(B), 45 _(C), 45 _(D). Each of the sub-streams flowing througha given set of oxidant (or fuel) tubes 45 _(A), 45 _(B), 45 _(C), 45_(D) recombines into a single stream of hot oxidant (or fuel) 13 _(A),13 _(B), 13 _(C), 13 _(D) (21 _(A), 21 _(B), 21 _(C), 21 _(D)) in anassociated chamber 49 _(A), 49 _(B), 49 _(C), 49 _(D). In this manner,the flows of hot oxidant (or fuel) 13 _(A), 13 _(B), 13 _(C), 13 _(D)(21 _(A), 21 _(B), 21 _(C), 21 _(D)) do not comingle with one anotherbut are kept separate by the dividers 39 and oxidant tubes 45 _(A), 45_(B), 45 _(C), 45 _(D), and dividers 59.

With continuing reference to FIGS. 7A-F, the oxidant (or fuel) andshell-side fluid are prevented from contacting one another by virtue oftubesheets 43, 47 separating the interior portion of the heat exchangerthrough which the hot shell-side fluid flows and through which theoxidant tubes 45 _(A), 45 _(B), 45 _(C), 45 _(D) extend from endportions constituting interior spaces 41 _(A), 41 _(B), 41 _(C), 41_(D), 49 _(A), 49 _(B), 49 _(C), 49 _(D). In other words, the feed endsand discharge ends of the oxidant (or fuel) tubes 45 _(A), 45 _(B), 45_(C), 45 _(D) are sealed from the hot shell-side fluid by the presenceof tube sheets 43, 47.

A variant of the shell and tube exchanger of FIGS. 7A-7F is bestillustrated in FIG. 7G where features are included that compensate fordifferences in thermal expansion between the shell and the various setsof oxidant (or fuel) tubes. When one or more of the oxidant flows, forexample oxidant flow 11 _(A), is decreased through the heat exchangerwhile the other oxidant flows, for example oxidant flows 11 _(B), 11_(C), 11 _(D), is kept unadjusted or increased, one of ordinary skill inthe art will recognize that the lower flow of oxidant 11 _(A) (throughassociated oxidant tubes 45 _(A)), will be heated to a relatively highertemperature than the higher flow of oxidant 11 _(B), 11 _(C), 11 _(D)(and associated oxidant tubes 45 _(B), 45 _(C), 45 _(D)). The highertemperature oxidant tubes 45 _(A) will experience thermal expansiongreater than that of the lower temperature oxidant tubes 45 _(B), 45_(C), 45 _(D). One of ordinary skill in the art will also recognize thatthe converse situation applies with equal force, namely: the flow rateof oxidant flow 11 _(A) is higher while that of oxidant flows 11 _(B),11 _(C), 11 _(D) are lower and oxidant tube 45 _(A) experiences lessthermal expansion than that of oxidant tubes 45 _(B), 45 _(C), 45 _(D)).If the differences in thermal expansion (and/or contraction) exceed thedegree to which the heat exchanger can withstand the resultant stresses,the seal between the oxidant tubes and tube sheets may burst or leak.

To compensate for the above differences in thermal expansion, the shell36 may be provided with an expansion joint 59. Also, each of the oxidant(or fuel) tubes 45 _(A), 45 _(B), 45 _(C), 45 _(D) in a set associatedwith flow of oxidant (or fuel) 11 _(A), 11 _(B), 11 _(C) (19 _(D), 19_(A), 19 _(B), 19 _(C), 19 _(B)) discharges into an associatedcollection space that is enclosed and sealed with a bonnet 53 _(A), 53_(B) (the bonnets associated with the other flows are not illustrated inFIG. 7G). Each of the bonnets 53 _(A), 53 _(B) (including those for theother flows) is connected to the shell 36 via an associated expansionjoint 55 _(A), 55 _(B) in order to accommodate the differing thermalexpansion/contraction.

In the variant of FIG. 7G, the heat exchanger is not provided with thedownstream tubesheet 47. Rather, the heat exchanger includes a “tubesheet-like” divider 48 that provides an imperfect seal in between, onone hand, the interior portion of the shell through which the hotshell-side fluid flows, and on the other hand, the space in between thedivider 48 and the downstream end of the shell 36. The divider 48includes orifices having a cross-section approximating those of theoxidant (or fuel) tubes 45 _(A), 45 _(B), 45 _(C), 45 _(D) only withwider dimensions so that the oxidant (or fuel) tubes 45 _(A), 45 _(B),45 _(C), 45 _(D) may slide through expansion or contraction through theorifices. Instead of using a tubesheet 47 to separate the hot shell-sidefluid from the oxidant (or fuel) in the collection spaces at thedischarge end of the heat exchanger, the combination of the oxidant (orfuel) tubes 45 _(A), 45 _(B), 45 _(C), 45 _(D) and the divider 48 keepsthe oxidant (or fuel) and hot shell-side fluid separate.

One of ordinary skill in the art will recognize that, while FIGS. 7A-7Gillustrate each set as including only four oxidant (or fuel) tubes 45_(A), 45 _(B), 45 _(C), 45 _(D) each, each set may include any numberthat is only limited by the complexity of manufacturing and/or cost ofmanufacture.

In one variation, each burner may also receive pre-heated oxidant (orfuel) from two heat exchangers. This enables a larger variation inoverall oxidant (or fuel) flow to the burner without imposing a highvariation in temperature at the burner. For example, for four burnerseach consuming 200 Nm³/hr of oxygen (or fuel), and two heat exchangerseach configured to pre-heat four oxidant (or fuel) flows, each heatexchanger may deliver 100 Nm³/hr of pre-heated oxidant (or fuel) to eachburner from each heat exchanger. Then, if it is required to reduce theoxidant (or fuel) flow to one burner to 100 Nm³/hr, one oxidant (orfuel) stream to that burner is shut off, and the flow of hot air to thecorresponding heat exchanger is reduced so as to maintain thetemperature of the remaining three flows. In this way the flow to oneburner can be reduced by a large factor without impacting thetemperature of the oxidant (or fuel) flowing to any burner.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims. The presentinvention may suitably comprise, consist or consist essentially of theelements disclosed and may be practiced in the absence of an element notdisclosed. Furthermore, if there is language referring to order, such asfirst and second, it should be understood in an exemplary sense and notin a limiting sense. For example, it can be recognized by those skilledin the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means thesubsequently identified claim elements are a nonexclusive listing i.e.anything else may be additionally included and remain within the scopeof “comprising.” “Comprising” is defined herein as necessarilyencompassing the more limited transitional terms “consisting essentiallyof” and “consisting of”; “comprising” may therefore be replaced by“consisting essentially of” or “consisting of” and remain within theexpressly defined scope of “comprising”.

“Providing” in a claim is defined to mean furnishing, supplying, makingavailable, or preparing something. The step may be performed by anyactor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

All references identified herein are each hereby incorporated byreference into this application in their entireties, as well as for thespecific information for which each is cited.

What is claimed is:
 1. A charge heating installation utilizingpre-heated oxidant, comprising: a system for recovering heat from afurnace, comprising: a source of oxidant having an oxygen concentrationgreater than that of air; a recuperator or regenerator, said recuperatoror regenerator adapted and configured to exchange heat between a flow ofshell-side fluid and a flow of combustion gases from a furnace toproduce a flow of heated shell side fluid; a first shell and tube heatexchanger comprising: a shell, a heated shell side fluid inlet and ashell-side fluid outlet formed in the shell thereof, first and secondoxidant inlets receiving first and second main flows of the oxidant,respectively, first and second oxidant inlet interior spaces receivingsaid first and second main flows of the oxidant, respectively, saidfirst and second oxidant inlet interior spaces being disposed entirelywithin said shell and being divided from one another by a divider, firstand second sets of oxidant tubes, the first main flow of oxidant beingdivided into a plurality of substreams equal in number to a number ofoxidant tubes in the first set, the second main flow of oxidant beingdivided into a plurality of substreams equal in number to a number ofoxidant tubes in the second set, the first set receiving the substreamsof the first main flow from said first oxidant inlet interior space, thesecond set receiving the substreams of the second main flow from saidsecond oxidant inlet interior space, each of the oxidant tubes extendingthrough an interior of the shell, an upstream tubesheet dividing saidfirst and second oxidant inlet interior spaces from an interior portionof said shell that each of the oxidant tubes extends through, first andsecond oxidant outlet interior spaces receiving said first and secondmain flows of the oxidant, respectively, from said first and second setsof one or more oxidant tubes, respectively, said first and secondoxidant outlet spaces being entirely disposed within said shell andbeing divided from one another by a divider, first and second oxidantoutlets receiving the first and second main flows of oxidant,respectively, from the first and second sets of oxidant tubes,respectively, via said first and second oxidant outlet interior spaces,respectively, and a downstream tubesheet or a downstream imperfectlysealed tubesheet-like divider dividing said first and second oxidantoutlet interior spaces from an interior portion of the shell that eachof the oxidant tubes extends through, wherein the first shell and tubeheat exchanger is adapted and configured to transfer heat from the flowof heated shell side fluid to the main flows of oxidant flowing throughthe oxidant tubes; wherein the system for recovering heat from a furnacefurther comprises: a first oxidant feed conduit fluidly communicatingbetween the source of oxidant and the first oxidant inlet; a secondoxidant feed conduit fluidly communicating between the source of oxidantand the second oxidant inlet; first and second oxidant flow controldevices disposed in the first and second oxidant feed conduits,respectively; first and second heated oxidant feed conduits receivingthe first and second main oxidant flows, respectively, from the firstand second oxidant outlets, respectively; first and second burnersreceiving first and second flows of heated oxidant, respectively, fromthe first and second oxidant feed conduits, respectively; a meltingfurnace containing a charge, each of the burners being operativelyassociated with the furnace such that the charge is heated throughcombustion of a fuel and heated oxidant injected by the burners, whereinthe recuperator or regenerator receives a flow of heated combustiongases from the combustion of the oxidant and fuel in the furnace toproduce the flow of heated shell side fluid; and a first controlleradapted and configured to control a flow rate of oxidant from theoxidant source through the first oxidant feed conduit and a flow rate ofoxidant from the oxidant source through the second oxidant feed conduitwith the first and second oxidant flow control devices, respectively,wherein one of a flow of the first oxidant through the first oxidantfeed conduit and a flow of the second oxidant through the second oxidantfeed conduit may be controlled by said first controller independentlyand separately from control of a different one of a flow of the firstoxidant through the first oxidant feed conduit and a flow of the secondoxidant through the second oxidant feed conduit so that a power of thefirst burner may be adjusted without requiring a concomitant andequivalent adjustment of a power of the second burner.
 2. Theinstallation of claim 1, wherein: the first and second oxidant inletsare disposed at one end of the shell and the first and second oxidantoutlets are disposed at an opposite end of the shell; and each of theoxidant tubes extends in a straight line from the first and secondoxidant inlet interior spaces to the first and second oxidant outletinterior spaces.